Typically, there are two types of keypads used in radiotelephones. In the first type of keypad, the keys are directly attached to the circuit board internal to the radiotelephone. In the second type of keypad, the keypad is a separate entity from the circuit board contained within the radiotelephone. The keypad and the circuit board are coupled together via wires. In either case, the keypad assembly takes up a significant volume of the radiotelephone, which is a disadvantage as the existing market trend is for smaller and smaller phones. As a reduction in size and increased requirement for design flexibility in radiotelephones becomes more prominent, efficient use of space become more important.
In the first type of keypad, the keypad utilizes a relatively large amount of space on the circuit board contained within the radiotelephone. Since the keypads interact directly with the circuit board, back-lighting each individual key is necessary because there is no use of reflective plates or light pipes, this increases the power consumption and makes the keypad more cumbersome.
In the second type of design, the keypad is separated from the circuit board internal to the radiotelephone except for the electrical coupling of the keypad circuitry to the circuit board. For example, a keypad containing twenty-four keys requires approximately thirteen wires plus the wiring for the backlighting circuitry. This second type of keypad supports backlighting with reflector plates or light pipes, which reduces the number of LEDs necessary to backlight a keypad. This second type of keypad also supports the use of conductive/resistive inks that allow circuits to be inked onto materials other than circuit boards themselves such as thermal plastics. However, the total size of the assembly is still bulky.
Moreover, in both cases the keys and key labels are fixed. Therefore, if a phone is to be configured to have Chinese language characters on the keys, then a complete change of keys are needed. This cannot be easily accomplished in the field, and is more suited to proper configuration at the factory. Along these lines, an end user cannot make cosmetic changes in the appearance in the keypad assembly if desired.
Although the two preceding designs have served the industry well to this point, the need exists for a keypad which is more efficient in the use of space. It would also be of benefit if the assembly allowed customizing or changing of the key labels in the field, or at the point of sale, without disassembly of the keypad thereby maintaining keypad integrity. It would also be an advantage to provide a lighted, low-profile solution while maintaining a low cost.